This project focuses on microRNA mechanisms on ocular angiogenesis. Angiogenesis plays a central role in eye development and also many major blinding retinal diseases, such as age related macular degeneration (AMD).The discovery of MicroRNAs as small endogenous RNAs regulating gene expression post-transcriptionally has revolutionized our understanding of genetic pathway networks, and ignited tremendous studies to explore microRNA therapeutics for numerous diseases. Our broad long-term goals are: (a) to understand the mechanisms of how specific microRNAs regulate ocular vascular development and (b) to decipher the roles of these microRNAs in vascular retinopathies. Our recent studies show that a specific microRNA, miR-126, is an endothelial cell specific microRNA regulating angiogenic pathways in response to vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF). We also have preliminary data that miR-126 is expressed specifically in the endothelium in the retina/choroid, and is required for sprouting retinal angiogenesis. Our organizing hypothesis for this proposal is that by regulating multiple angiogenic pathways miR-126 plays a critical regulatory role in ocular angiogenesis and in the pathogenesis of neovascular AMD. As a small molecule with multiple regulatory functions, miR-126 would be an attractive therapeutic target for blinding vascular retinopathies. Specific Aim I is to define the expression pattern and regulation mechanism of miR-126 in the retina/choroid. Specific Aim II is to identify the requirement and mechanism whereby miR-126 regulates retinal vascular development. Specific Aim III is to determine the mechanism by which miR-126 regulates neovascularization in a laser induced choroidal neovascularization model.